The present invention relates to a multilayer structure which displays the same draining properties as prior art non-woven fabrics and high strength under low distortion or elongation (15% or less) conditions.
In construction works undertaken in the field of civil engineering, in particular, in anti-flood afforestation works, riparian works, road construction works, or the construction of structures on soft ground, synthetic resin drainage materials or reinforcing materials are sometimes spread over the bottom or inner zone of an earth structure or a building for the purpose of improving the operational efficiency and stability after construction has been completed.
However, none of these synthetic resin materials excel in both draining and reinforcing properties, each only satisfying one or the other to an adequate extent. Some materials may be regarded as satisfactory in both aspects to a certain degree. In such cases, however, the significance of one of these two categories of properties is only like that of an accessory with respect to the other.
In earth structures or building bases, any deformation of a structure due to distortion of about 5% to 15% is judged to be indicative of its breakdown or its ceasing to function as designed. Synthetic resins exhibiting a distortion rate in the range 5% to 15% (as shown by the results of a distortion test as set forth in JIS L-1096) are conventionally employed as reinforcing materials. The problem with these conventionally used synthetic resin materials which have a distortion rate in the above range and which exhibit a high strength is that they only provide poor draining properties.